For stream sockets, the connect() call attempts to establish a connection between two sockets. For UDP sockets, the connect() call specifies the peer for a socket. The s parameter is the socket used to originate the connection request. The connect() call performs two tasks when called for a stream socket. First, it completes the binding necessary for a stream socket [in case it has not been previously bound using the bind() call]. Second, it attempts to connect to another socket.

The connect() call on a stream socket is used by the client application to connect to a server. The server must have a passive open pending. If the server is using sockets, this means the server must successfully call bind() and listen() before a connection can be accepted by the server using accept(). Otherwise, connect() returns -1 and errno is set to ECONNREFUSED.

If s is in blocking mode, the connect() call blocks the caller until the connection is set up, or until an error is received. If the socket is in nonblocking mode, then connect() returns -1 with errno set to EINPROGRESS if the connection can be initiated (no other errors occurred). The caller can test completion of the connection setup by calling select() and testing ability to write to the socket.

When called for a datagram or raw socket, connect() specifies the peer with which this socket is associated. This gives the application the ability to use data transfer calls reserved for sockets that are in the connected state. In this case, read(), write(), readv(), writev(), send(), and recv() calls are available in addition to sendto(), recvfrom(), sendmsg(), and recvmsg() calls. Stream sockets can call connect() only once, but datagram sockets can call connect() multiple times to change their association. Datagram sockets can dissolve their association by connecting to an incorrect address, such as a null address (all fields cleared).

#include <manifest.h>
#include <bsdtypes.h>
#include <socket.h>
#include <in.h>
int connect(int s, struct sockaddr *name, int namelen)

Parameter

Description

s

Socket descriptor

name

Points to a socket address structure containing the address of the socket to which connection will be attempted

namelen

Size of the socket address, in bytes, pointed to by name

The name parameter points to a buffer containing the name of the peer to which the application needs to connect. The namelen parameter is the size, in bytes, of the buffer pointed to by name.

Related information

Servers in the AF_INET domain

struct in_addr
{
        u_long s_addr;
};
struct sockaddr_in
{
        short   sin_family;
        u_short sin_port;
        struct  in_addr sin_addr;
        char    sin_zero[8];
};

The sin_family field must be set to AF_INET. The sin_port field identifies the port to which the server is bound; it must be specified in network byte order. The sin_addr field specifies a 32–bit Internet address. The sin_zero field is not used, and must be set to all zeros.

Servers in the AF_IUCV domain

struct sockaddr_iucv
{
    short           siucv_family;    /* addressing family */
    unsigned short  siucv_port;      /* port number */
    unsigned long   siucv_addr;      /* address */
    unsigned char   siucv_nodeid[8]; /* nodeid to connect to */
    unsigned char   siucv_userid[8]; /* userid to connect to */
    unsigned char   siucv_name[8];   /* iucvname for connect */
};

Return values

Related calls

bind(), htons(), inet_addr(), listen(), select(), selectex(), socket()